How to reset Dell 2335dn MFP laser printer's authentication password?

Hi,

I'm Dhananjay and I work as an IT technician for Smartway Pharmaceuticals, UK. 

A few days back somebody changed the password for Dell 2335dn MFP's Web Embedded Service. Printer started giving some issues when we switched to another ISP (I don't know whether switching of ISP might cause a problem to the networked printer!). Now when I try to update any changes made to settings using Embedded Web Service (Web interface to change settings of printer), a pop-up window comes up requesting for an authentication (similar window when we try to login to router) Refer to the attached screenshot..

It never used to pop-up such window so far. I haven't changed any username or password. How to reset this password? I tried calling Dell support they suggested me to Restore all options - done that, Performed All Clear Memory reset as well using below steps:

1. On panel Selected Directory > # > 1 > 9 > 3 > 4 > Tick 
2. Selected Tech Menu > Data Setup > Clear All Memory
3. Cleared all memory but still the issue don't go!

Please HELP! URGENT!! I want to change some FAX settings on it.

Many Thanks in advance..!!